Polyester resins, which are polycondensation products of polycarboxylic acids with polyhydroxyalcohols (polyols), are conventionally preparable in the form of unsaturated structures which can be cross linked through their double bonds with a compatible monomer, and thus made thermosetting. Typical unsaturated polyesters are made by condensing dihydroxyalcohols with dicarboxylic acids, at least a portion of such acids containing ethylenic unsaturation. Usually, unsaturated polyester resins are prepared and sold commercially as solutions of unsaturated polyester in a liquid vinyl monomer. Such a solution can be hardened (cross-linked) into a solid form under controlled conditions in the substantially complete absence of water typically involving the use of an initiator admixed in small quantities therewith, though, in general, such a solution can be hardened by means of light, heat, and/or free radicals.
Because of the characteristic low viscosity of such solutions, it is difficult to make such stay-put during application thereof, as in lay-ups thereof in combination with fiberglass in making wall portions of boats, storage tanks, truck cabs, and the like. Heretofore, the art has only been able to control the viscosity of such solutions through the addition thereto of controlled amounts of fumed silica (pyrogenic silica) which result in a thickening of such solutions.
The use of fumed silicas in liquid polyester resin systems has disadvantages and causes problems. For one thing, fumed silicas characteristically have a low density and tend to cause dust in areas of use which can produce a health hazard to exposed personnel. Even with best practice, the use of inconvenient respiration masks are required. In addition, fumed silicas must be incorporated into a liquid resin system with high shear mixing equipment which appreciably adds to the cost and time involved in liquid unsaturated polyester resin manufacture.
In addition, the presence of fumed silica in a liquid curable polyester system prevents the production of clear solid polyester resin products therefrom which is undesirable in some circumstances because a plurality of end use applications exist where clear solid polyester resins are needed or desired; such as where pigments are to be added and no change in optical properties is desired.
Also, fumed silicas in cured polyesters tend to reduce the chemical stability thereof apparently because of a type of "wicking" action caused therewith, plus the hydrophylic nature of the fumed silicas.
Further, fumed silicas behave in liquid polyester solutions as fillers. Thus, while they can add to the mechanical structure of a cured product, they do not become part of the molecular structure of such product. For example, in some applications, the fumed silica, in effect, causes a fabricator to sacrifice incorporating a maximum quantity of fibrous reinforcing filler into a lay-up which would otherwise be a greater amount of such filler if there were not a requirement for using fumed silica in his lay-up liquid resin in order to achieve the viscosity characteristics he needs for stay put during a fabrication procedure.
In view of the problems and disadvantages of employing fumed silicas in curable liquid unsaturated polyester systems, the art needs alternative means for controlling the viscosity characteristics of such liquids, and hopefully, for also improving the physical properties of the resulting cross-linked (cured) solid products derived therefrom.
So far as is known, no one has heretofore employed organoaluminum compounds in anhydrous unsaturated polyester systems dissolved in liquid vinyl monomers. If water is present, the aluminum compound reacts therewith, not with the polyester resin system. Thus, while Okada et al in Japanese Pat. No. 74/16,792 (application No. 72/55,390 filed June. 1, 1972) describe water containing polyester moldings which are hardenable in the presence of an aluminum alkoxide and an initiator, no one has ever heretofore used aluminum alkoxides in anhydrous unsaturated liquid polyester systems or made cured resins therefrom. The reactions involved and the results obtained in the latter instance are surprising and unexpected compared to such prior art as represented by Okada et al.
Ko et al in Japanese Pat. No. 74/93,424 used aluminum complexes as hardening agents for a methylmethacrylate copolymer differing from the present invention in that the quantity used produced hardening or curing. The same is true of Japanese Pat. No. 74/32,676, in which aluminum chelates were used as a polymerization catalyst to produce a poly-(ethylene terephthalate). The aluminum octanoate of Japanese Pat. No. 73/90,382 differs from the aluminum derivatives of this present invention in that the aluminum octanoate is a basic aluminum salt. Japanese Pat. No. 71/40,713, uses aluminum alkoxides as catalysts for preparing polyesters, making use of the well known ability of aluminum alkoxides to catalize ester exchange reactions. Jacobus Rinse in U.S. Pat. No. 3,141,007 uses massive amounts of aluminum isopropoxide with maleic anhydride and methylmethacrylate to form a composition in which the aluminum compounds have participated as ingredients and also as polymerization catalysts. In British Pat. No. 920,902, Watanabe et al used aluminum alkoxides to produce a stable solid gel for molding materials in the form of sheets or blocks.
None of the prior art above teaches the principles employed in the present invention, which involve use of organic aluminum derivatives in an anhydrous wholly liquid unsaturated polyester resin system, at temperatures from ambient to about 100.degree. C. to produce a non-Newtonian liquid whose thixotropic character allows it to be conveniently used for laminating, spraying, hand lay-up, and the like, and further producing a cured resin with superior chemical resistance properties. See also, Japanese Pat. No. 36(9), 423-8, 1963.
The use of organoaluminum compounds in unsaturated polyester resins is to be distinguished from the use of organoaluminum compounds in alkyd resins. For one thing, alkyd resins employ fatty acids while unsaturated polyester resins do not. For another thing, alkyd resins characteristically employ tri and tetra functional polyols while unsaturated polyester resins employ primarily difunctional polyols. For still another thing, alkyd resins cure by oxidation polymerization, not addition polymerization as in the case of unsaturated polyester resins. Also alkyd resins are used primarily in coating type application situations whereas unsaturated polyester resins characteristically are used primarily in molding applications. The technology of alkyd resins is thus not equivalent to that of liquid unsaturated polyester resin systems.